Search

Large volume changes and low electronic conductivity limit the advancement of mixed metal vanadate oxides as anode materials in lithium-ion batteries. Herein, ultrafine Co3V2O8 nanoparticles with a diameter of 7–9 nm are embedded in situ within the walls of hollow carbon combination spheres (HCCSs) through spray drying and calcination process. Each unit sphere of HCCS has an internal cavity of 170 nm and a wall thickness of 12 nm. When tested in lithium-ion half-cells, Co3V2O8/HCCS sustains a high reversible capacity of 1043 mAh g–1 at 0.2 A g–1 after 120 cycles, 832 mAh g–1 at 0.5 A g–1 after 580 cycles, and 759 mAh g–1 at 1.0 A g–1 after 800 cycles. Kinetics investigation uncovers a noticeable pseudocapacitive effect. Li+ diffusion coefficient ranges from 1.12 × 10–12 to 6.62 × 10–14 cm2 s–1. Electrochemical impedance spectroscopy revealed low Ohmic resistance and charge transfer resistance, confirming efficient Li+ diffusion. The full cell also exhibits excellent cycling performance and rate capability. The exceptional electrochemical performance is associated with the unique hollow carbon combination sphere and the embedded structure of ultrafine Co3V2O8 nanoparticles. The former improves the structural strength, facilitates ion transport and electronic conduction, and prevents Co3V2O8 detachment from the composite. The latter further suppresses the volume variation of Co3V2O8 and enhances its electrochemical activity. [ABSTRACT FROM AUTHOR]

This work systematically studied the corrosion behavior and passivation property of CoCrFeNi high‐entropy alloys (HEAs) in a simulated seawater environment. The results reveal that the addition of CO32−/HCO3− results in the secondary passivation of the HEA in NaCl solution, and secondary passivation film possesses higher dissolution rate in comparison with primary passive film. H+ ions ionized by HCO3− facilitate the charge transfer process, thin the thickness of passive film, and increase the disordered degree of the film. Moreover, the presence of HCO3− promotes the nucleation and growth of metastable pits, and enhances the pitting sensitivity. Furthermore, an increase in CO32− concentration accelerates the dissolution of passive film, weakens the compactness and protective performance of the film, and increases the probability that metastable pitting evolves into stable pitting, as well aggravates the corrosion of the HEA. In addition, the corrosion resistance of the HEA is diminished due to the formation of microgalvanic corrosion cells between matrix and inclusion. The selective dissolution of elements occurred in the HEA. [ABSTRACT FROM AUTHOR]

Monodispersed and faceted Bi2Fe4O9 micro-cuboid crystals with a mullite-type structure have been successfully synthesized by a facile hydrothermal method. The single crystalline Bi2Fe4O9 micro-cuboids exhibited a length of 10–20 μm and a square cross-section with a side length of 1–2 μm. The preferential growth of the Bi2Fe4O9 micro-cuboid crystals has been determined to be along 〈001〉 with the dominant (110) and (−110) facets enclosed. These micro-cuboid crystals were probably formed by a dissolution–recrystallization mechanism, where a phase transition from irregular-shaped sillenite Bi25FeO40 agglomerates to perovskite BiFeO3 microspheres occurred and finally resulted in the micro-cuboid crystals. More interestingly, these micro-cuboids demonstrated a remarkable photo-Fenton catalytic degradation activity towards RhB under visible light irradiation (λ > 400 nm). 90.2% RhB decomposition at 120 min can be achieved and the corresponding apparent rate constant is 0.0175 min−1, 11.67 times and 3.65 times larger than that of Fenton-like oxidation and pure photocatalysis, respectively. The as-prepared Bi2Fe4O9 micro-cuboid crystals also showed intriguing morphology-dependent ferromagnetism at room temperature, possibly allowing the magnetic recollection and reuse of Bi2Fe4O9 samples as well as their magnetic-field-mediated photocatalytic performances. [ABSTRACT FROM AUTHOR]

The corrosion behaviour and mechanism of CoCrNi medium-entropy alloy (MEA) imposed by alternating current (AC) in HCO3−/CO32− solution with various pH were systematically investigated via a series of corrosion tests. The results showed that with the augment of pH value, the polarisation resistance of the MEA decreased significantly, Ep shifted negatively, and ipI value increased, as well as corrosion rate was enhanced, revealing that the corrosion resistance was weakened. As solution pH increased, the formation of secondary passivation zone became easier, which may be attributed to the reaction conversion process of Cr(III) to Cr(VI) species. Moreover, the increase in pH led to an increase in defect density and a thinning of passivation film, facilitating the corrosion of the MEA. AC interference accelerated the ion exchange process and promoted the formation possibility of stable pitting. Higher iAC and pH inhibited the repassivation of metastable pitting, and increased the pitting susceptibility. Highlights The effect of pH on the corrosion behaviour of CoCrNi MEA with imposed AC was clarified. High pH and iAC accelerated the nucleation and growth of metastable pits. With increased pH and iAC, the stability and protective ability of passive film were weakened. The secondary passivation of the MEA was mainly due to the conversion of Cr(III) to Cr(VI) species. [ABSTRACT FROM AUTHOR]

The corrosion behavior and mechanism of CoCrFeNi HEA under AC application were systematically studied in 3.5 wt.% NaCl solution containing different concentrations of NaHSO3. The results showed that the existence of HSO3− increased the defect density within the passivation film on the surface of the HEA. With the increase of HSO3− concentration, the passivation zone became narrow, Ep shifted negatively, and ip increased, which indicated that the corrosion resistance of the HEA was weakened. When the HSO3− concentration increased to 0.1 M, a clear transition zone appeared, indicating that the increase in concentration reduced the passivity of the HEA, and its corrosion behavior changed from the typical passivation characteristic to the activation state with increasing iAC. The imposed AC promoted the nucleation of metastable pitting, which was indicated by a remarkable increase in the average pitting number density (Navg) from 5 to 17 mm−2 with the enhancement of iAC. [ABSTRACT FROM AUTHOR]

To develop marine simulators of Small Waterplane Area Twin Hull (SWATH) ships and gain a better understanding of the maneuverability of the SWATH, a mathematical model with five Degree of Freedom(DOF)for SWATH has been established, in which the surge, sway, yaw, roll and pitch motions are all considered. The characteristics of the SWATH ship form and the hydrodynamic interaction among the twin bodies, twin propellers and twin rudders are taken into consideration on the basis of the three DOF maneuvering mathematical model. To verify the effectiveness of the modeling and ensure the use of the model in marine handling simulators, a detailed model is tentatively established on the basis of empirical formulas. Based on the acquired results, tests were performed to simulate the steady turning and zigzag motions of the ship. The results are in accordance with regular pattern and trend of motion of SWATH ships. This verifies the effectiveness of the mathematical model of the turning movement.